Probing F-region thermosphere with ionospheric heater emissions

Fabry-Perot interferometers are used to make ground-based observation of the neutral winds by imaging the natural airglow that occurs from photochemical processes in the thermosphere. FPIs with suitable spectral resolution can be used to estimate the line-of-sight bulk motion using the Doppler shift of the emission, and the in-situ temperature using the broadening of the emission line. When observing emission from thermospheric species, these observations give estimates of the wind speed and temperature. For the airglow red-line atomic oxygen emission at 630.0 nm this occurs at altitudes of around 240 km. During operation of ionospheric heaters, artificial excitation of this emission is often produced, but at lower altitudes of 120-180 km, a region with few natural airglow emissions. The lack of natural airglow in this altitude region makes using ionospheric heater emissions to conduct FPI observations highly attractive, since sounding rocket or satellite based observations of the winds in this region are expensive compared to ionospheric heating experiments and ground-based observations. Since the most intense and common heater emission is the 630.0 nm oxygen red-line, any observation of the heater spot will also include natural airglow (and possibly aurora emissions). The analysis of the heater observations must account for this background emissions. The wind estimation from FPI analysis of multiple emissions was found to be approximately the geometric mean of wind conditions in each emission region, weighted by the intensity of emission of each region. Using a background observation of only the natural airglow, this model of multiple emissions allows the wind characteristics of just the ionospheric heater emission region to be estimated. A Monte-Carlo simulation was performed to determine how well the model predicts single emission characteristics from a multiple emission image and a background image. These results will be presented as well as a comparison to closed form minimum conditions to confirm ionospheric heater emission observation.